System.NullPointerException: Attempt to de-reference a null object

System.NullPointerException: Attempt to de-reference a null object

How to solve System.NullPointerException: Attempt to de-reference a null object error

System.NullPointerException: Attempt to de-reference a null object is very common error in apex class. It occurs when your variable (sobject, list, set or any other data type) is not initialized (allocated memory). In order to use the non primitive data type in the code we need to initialize the memory first. If we don’t do that it may result in Attempt to de-reference a null object error. This error may occur in Apex classes, Visualforce pages with Apex controller, Test classes, Apex Triggers.

For Example if I use like this:

Account acc;
acc.Name = 'sfdcpoint';

It will result in attempt to de-reference a null object error.

We should use it like this:

Account acc = new Account();
acc.Name = 'sfdcpoint';

When we use list or set then also we need to allocate memory to list or set like this